After a certain point, Mana ramp cards basically become useless, so playing Hemet on curve and before you drop Barnabus guarantees you will get nothing but big minions from then on out (or card draws like Nourish, or other high level cards like Moonglade portal). Of course you have to play Hemet BEFORE you drop Barnabus or you'll destroy you entire deck (They actually changed that though: Before it destroyed cards based on their old cost, not it destroys the zero cost ones too).